1/2 pound freshly ground lamb, well chilled
1/2 pound freshly ground beef chuck, well chilled
3 ounces pork fatback or bacon, diced and well chilled
1 teaspoon minced garlic (about 1 medium clove)
2 teaspoons kosher salt
1/3 cup finely minced red onion
1/2 teaspoon dried oregano, preferably Greek
1/2 teaspoon freshly ground black pepper
9 slider-size potato rolls, split
Pickled peperoncini, for topping